1. Field of the Invention
The present invention generally relates to an apparatus and a method for depositing a low dielectric constant film. More particularly, the present invention relates to an apparatus and a method for depositing a low dielectric constant amorphous hydrogenated carbon film utilizing high density plasma chemical vapor deposition (HDP-CVD).
2. Background of the Related Art
Consistent and fairly predictable improvement in integrated circuit design and fabrication has been observed in the last decade. Recent increases in ultra large scale integration (ULSI) and the corresponding decreases in the dimensions of the electrical devices have increased the inter-level and the intra-level capacitances which in tun cause an increase in signal delays that hinder the performance of the devices. With newer ULSI operation frequencies approaching 1 GHz and interconnect feature sizes decreasing to less than 250 nanometers, the interconnect resistance-capacitance (RC) delay becomes a major determinant to the speed of the integrated circuits. Significantly new and different manufacturing approaches will be required to achieve the required performance and speed goals. Since RC delay is directly related to the interconnect resistance and dielectric capacitance, the industry focus is on developing new materials with significantly lower dielectric constants and lower resistivities.
In the area of dielectrics, a great variety of materials are being investigated as potential replacements for the current standard silicon dioxide (SiO2). In order to improve the performance of the new ULSI circuits, insulating materials having dielectric constants (k) significantly lower than that of the silicon dioxide (k≈4) are needed to reduce the RC delay and cross talk. It is well accepted that a dielectric constant of less than 3.0 will be required for the next generation of sub-micron devices in order to meet the expected performance requirements.
A great variety of materials with low dielectric constants are being investigated as potential candidates to replace SiO2. However, it is important to remember that the dielectric constant is only one of many critical requirements that must be met. Ease of integration into existing and future process fabrication flows and economic factors (e.g., cost of ownership) will together decide the viability of a material for use as the next generation intermetal dielectric (IMD). Integration capability will be determined by critical properties such as adhesion, thermal stability, thermal conductivity, mechanical strength and gap fill performance. Cost of ownership will be determined by cost of the raw materials, cost of processing waste material (which has been found to be especially high with spin-on techniques), the number of required integration steps as well as the capital cost of the processing equipment. The ideal low dielectric constant material will easily integrate into existing process flows, utilize existing equipment, and cost no more than currently used processes.
Chemical vapor deposition (CVD) appears to be the most promising approach to form low dielectric constant materials. It is well accepted that the mechanisms in plasma assisted depositions will lead to materials with significantly higher density and mechanical strength than other types of deposition techniques. In addition, integration of a CVD film is well characterized and fairly simple to implement as compared to wet processes such as spin-on methods. The potential of using existing plasma enhanced CVD equipment and simple manufacturing methodology makes CVD materials attractive from both an integration and an economic standpoint.
Among the CVD-deposited materials, hydrogenated amorphous carbon (xcex1-C:H) films, also called diamond-like carbon (DLC) films, have shown great potential for applications as low dielectric constant materials used in structures and devices in ultra large scale integration (ULSI). However, integration of the dielectric material into ULSI circuits requires thermal stability of the dielectric material at temperatures of at least about 400xc2x0 C. Similar to other low dielectric constant materials, such as polytetrafluoroethylene (PTFE) with k≈2.0, hydrogenated amorphous carbon films have been found to be unstable at temperatures above about 350xc2x0 C. and have failed to retain their low dielectric constant property. The hydrogenated amorphous carbon films that have been found to exhibit high thermal stability at temperatures greater than about 350xc2x0 C. typically possess dielectric constants of about 6.0, which is unacceptable for use in ULSI circuits.
An alternative to the hydrogenated amorphous carbon films incorporates fluorine into a DLC film. One such fluorinated DLC film has been described by A. Grill, V. Patel and C. Jahnes, in xe2x80x9cNovel Low k Dielectric Based on Diamondlike Carbon Materials,xe2x80x9d J. Electrochem. Soc., Vol. 145, No. 5, May 1998. However, the incorporation of fluorine during the film formation complicates the deposition process. One problem associated with the fluorinated DLC films is that organic fluorocarbon molecules will either form etching species or polymerize under glow discharge conditions. Whether the etching species formation or the polymerization reaction dominates depends on the plasma energy, the charged specie intensities, the reactant ratios and the surface temperatures. In either case, the material properties of the resulting film are degraded by these reactions. Another problem encountered is that fluorine generated during deposition of the fluorinated DLC may be absorbed by the chamber walls and chamber components. The fluorine incorporated into the surface of the chamber walls and chamber components increases the chamber cleaning time. The prolonged cleaning time results in a decrease in throughput of the processing system.
The sub-micron interconnect features in the next generation of ULSI integrated circuits also demand precisely patterned photoresist to properly etch the structures of the interconnect features into a dielectric film, such as an intermetal dielectric layer. Generally, to form an interconnect feature in a dielectric film on a substrate, a photoresist is applied over the surface of the dielectric film and patterned using a light source, preferably a light source using ultraviolet (UV) wavelengths. Typically, the UV light source uses wavelengths of about 193 nm or about 248 nm to pattern the photoresist for sub-micron features. After the photoresist has been patterned, the substrate is etched using commonly known etching techniques to form the interconnect structures in the dielectric film.
An anti-reflective coating (ARC) is typically deposited on the dielectric film prior to the application of the photoresist. The ARC film reduces the reflections of the UV light source during the patterning process to provide sharper definitions to the patterns on the photoresist. However, currently practiced ARC films do not provide adequate anti-reflective properties for the 193 nm and 248 nm UV wavelengths. The patterns on the photoresist are distorted by the reflections of the UV light from the substrate surface, particularly reflection from the metal deposited on the substrate, resulting in poorly defined interconnect features after the etch process. Poorly defined interconnect features leads to improper and defective device formation on the substrate.
Therefore, there is a need for a method of forming a hydrogenated amorphous carbon film that is useful in the fabrication of ULSI circuits. It would be preferable for the hydrogenated amorphous carbon film to possess a dielectric constant less than about 3.0 as well as exhibit high thermal stability at temperatures greater than about 400xc2x0 C. It would be further desirable for the hydrogenated amorphous carbon film to provide low reflectance to UV light, particularly for the 193 nm and 248 nm UV wavelengths useful for patterning sub-micron interconnect features.
The present invention generally provides a method for depositing a low dielectric constant hydrogenated amorphous carbon film on a substrate or other workpiece using high density plasma chemical vapor deposition (HDP-CVD) techniques. Specifically, the present invention provides a method for forming a low dielectric constant hydrogenated amorphous carbon film having a dielectric constant of less than about 3.0 and a high thermal stability at a temperature of about 400xc2x0 C. or higher that is useful in the fabrication of ULSI circuits.
In one aspect of the invention, the method generally comprises positioning the substrate in a high density plasma chemical vapor deposition chamber, introducing a processing gas comprising a hydrocarbon gas and argon into the chamber, and generating a high density plasma of the processing gases to cause deposition on the substrate. Preferably, during the deposition process, the chamber pressure is maintained at between about 10 mT and about 100 mT, and the source RF power is applied at between about 1000 W and about 2000 W (for a 200 mm substrate) to the chamber. The substrate having the deposited carbon film thereon is then annealed at between about 300xc2x0 C. and about 430xc2x0 C. for between about 30 minutes and about 90 minutes in a vacuum environment or in an inert gas environment.
In a preferred embodiment, the film is deposited using methane (CH4) and argon in a HDP-CVD reactor. The resulting low dielectric constant amorphous carbon film is thermally stable at temperatures of at least about 400xc2x0 C. and has a dielectric constant (k) of about 2.53. The amorphous carbon film formed according to the invention is useful for many applications in ultra large scale integration (ULSI) structures and devices, such as an inter-metal dielectric material. The amorphous carbon film formed according to the invention is also particularly useful as an anti-reflective coating to provide low reflectance to UV light, particularly for the 193 nm and 248 nm UV wavelengths useful for patterning sub-micron interconnect features.